The present invention relates to a head suspension assembly in an information storage system, such as a magnetic disc drive. In particular, the present invention relates to a method of reducing deformation of a load beam and a gimbal induced by a welding process used to join them together.
In a magnetic disc drive, information is stored in the form of magnetically polarized bit positions on the surface of a rapidly rotating magnetic disc. Information is written to the disc and read from the disc by a transducer which is mounted on an air bearing slider. Information bit positions are arranged in generally concentric data tracks on the disc. The data tracks are further subdivided into sectors for ease of information organization.
The transducer and air bearing slider are collectively referred to as the head. The head flies in close proximity (5 to 10 micro inches) to the disc's surface, precisely balanced between hydrodynamic forces developed by the slider and an applied preload spring force.
As the disc rotates, hydrodynamic drag causes a thin layer of air molecules to remain essentially stationary relative to the disc's surface. This air layer is pulled under ski surfaces of the slider and induces high air pressure under them. The high air pressure under the slider generates a lifting force which keeps the head suspended over the magnetic disc.
The head should be supported in a manner which allows it to pitch, roll and move perpendicularly to the disc surface in order to follow small irregularities of the disc surface. In contrast, the head should be rigidly fixed in the plane of the disc surface in order to avoid off-track read errors.
A head support and suspension assembly precisely positions the head over the magnetic disc. The suspension assembly provides a precisely controlled preload spring force to the head, as well as freedom of motion about pitch and roll axes and normal to the plane of the disc's surface. Motion about the head's yaw axis, as well as in the in-plane directions is reduced, to the extent possible, by making the support assembly rigid in those directions.
The support and suspension assembly which moves and positions the head consists of three components. The first component is a rigid support arm which pivots on a servo spindle, firmly supporting the rest of the assembly as well as precisely controlling movement of the head in a radial direction over the surface of the disc.
The second component of the head support and suspension assembly is a load beam which is attached to the rigid support arm. The proximal end of the load beam, attached to the rigid support arm, is resilient in a direction normal to the disc surface. This resiliency is combined with a preformed bend to provide a preload spring force. In this way, the load beam pushes the head towards the disc surface while still permitting it to move and follow the topography of the disc.
The load beam has a rigid portion, the rigidity being achieved by stiffening channels or other bracing methods. The rigid portion transmits the preload spring force to the distal end of the load beam where the gimbal and head are attached. Additionally, the rigid portion of the load beam provides stable positioning of the head in all directions in the plane of the disc surface.
The third component of the head support and suspension assembly is a gimbal which connects the distal end of the load beam to the head. The gimbal is resilient in the head's pitch and roll directions to allow the slider to follow the topography of the disc which it is flying over. Also, the gimbal is rigid in the yaw and in-plane directions to maintain precise in-plane head positioning. The head and gimbal together are often referred to as the head-gimbal assembly.
There has been a continual drive to increase information storage density of disc drives. Minimum head to disc separation has become a critically limiting factor in the maximum storage density attainable. Head to disc separation is governed, to a large extent, by the characteristics of the head and support suspension assembly and the variation of said characteristics. Unwanted variation of the head and suspension assembly can induce undesirable forces and moments on the air bearing surfaces of the sliders. The direction and magnitude of the applied moments are a function of the suspension's static attitude.
The static attitude is the position the head takes in relation to the fastening points of the resilient end of the load beam when no forces are applied to the head. The static attitude, together with the spring constant of the gimbal, control the magnitude and direction of the applied moments on the head. This, in turn, has a major affect on the head-to-disc spacing and the characteristics of the head support and suspension assembly.
Two critical components of the static attitude are the pitch and roll static angles. These angles can be defined as the angles between the plane of the disc surface and the plane of the slider ski surface that would occur if the disc were not present (i.e. if no normal force were applied to the head by the disc). The pitch static angle is a primary determinate of the angle of the surface of the slider relative to the disc surface and thus is critical to the flying height of the head. The roll static angle controls the levelness of the head's flight and the relative heights of the two slider skies and thus can also affect the transducer's height. In addition, applied pitch and roll moments can cause extended dragging time of the slider along the disc during start-up of the disc drive.
Ideally, the suspension assembly should load the head against the disc such that no pitch or roll moments are applied to the head. Moments are usually created by either a damaged gimbal or the natural variation of the components due to manufacturing processes. When the head is loaded to the disc, the gimbal deflects to allow the removal of the pitch static angle and the roll static angle. The gimbal's resistance to this deflection is the direct cause of pitch and roll moments on the slider. These moments have been found to account for as much as 90% of the variation in slider fly height, pitch attitude, and roll attitude; which in turn affects the electrical output of the transducer and the reliability of the data storage process.